This invention relates to an annunciator, specifically to a microprocessor-based annunciator with an internal tachometer.
Annunciators are used for control and protection of remotely located internal combustion engines. Annunciators monitor a plurality of sensor inputs indicative of various engine parameters, such as oil pressure, water temperature, and engine speed. If one of these parameters is out of range, the annunciator triggers the shutdown of the engine and displays the fault condition, generally according to a sensor number. It is particularly important to monitor engine speed, because of the damage to the engine that can occur in a short period of time if engine speed exceeds acceptable levels.
Such remotely located engines are prevalent in oil field and pipeline locations where there may not be a readily available electric power supply. In such instances, annunciators must draw sufficiently low current to be powered from the Capacitor Discharge (CD) ignition of the engine being monitored or a magnetic pickup installed on the flywheel, and backed up by a small long life battery. In the field, CD ignitions are only able to supply a minimal amount of power to auxiliary equipment. Because of this, the drain or load of an annunciator must be minimal to avoid affecting the efficiency of the ignition system, especially during starting periods. Likewise since magnetic pickups are used to provide tachometer inputs, the drain or load of an annunciator must not degrade the pickup signal.
U.S. Pat. No. 4,336,463, expressly incorporated herein, discloses such a low power annunciator designed with digital logic. It is a disadvantage of such an annunciator, however, that it requires an external tachometer to monitor engine speed. External tachometers draw current and place an additional load on the ignition. Other disadvantages include increases in instrument count, instrument panel size, and instrument wiring, all of which increase overall instrument panel cost. A further disadvantage of using an external tachometer is the increased complexity of the overall system.
Incorporating a tachometer with an annunciator requires the addition of several logic functions including the sequential display of engine speed and fault conditions. The number of components required using digital logic makes the design approach prohibitive. While microprocessor-based annunciators operating at high speeds, such as Frank W. Murphy""s S1501, can be programmed to perform the necessary logic and control the display, they draw too much current to be powered from a CD ignition or magnetic pickup. And while microprocessor-based annunciators operating at low speeds, such as Frank W. Murphy""s Mark III and that disclosed in U.S. Pat. No. 5,563,456, expressly incorporated herein, draw sufficiently low current, their processing power is too limited to perform the necessary tachometer functions. Recent developments in technology, however, have resulted in peripheral-rich microprocessors that can be operated at low speeds with extremely low current draw and are capable of performing the necessary tachometer and display functions. Such a microprocessor is utilized in the present invention.
It is therefore an object of the present invention to provide a microprocessor-based annunciator with an internal tachometer that draws sufficiently low current to be powered from a CD ignition or magnetic pickup. The internal tachometer may advantageously include an overspeed shutdown setpoint and an underspeed shutdown setpoint.
It is a further advantage of the present invention that the internal tachometer can be easily calibrated to match timing pulses from the CD ignition of various engines or magnetic pickup pulses from various flywheels.
It is yet another advantage of the present invention that in addition to monitoring engine speed, it may also monitor engine run hours. U.S. Pat. No. 4,181,883, expressly incorporated herein, discloses an hourmeter-tachometer similar to Frank W. Murphy""s SHD30. It is an object of the present invention to provide an annunciator that incorporates the hourmeter-tachometer features of U.S. Pat. No. 4,181,883.
It is yet another advantage of the present invention that it can accommodate normally open or normally closed sensor inputs without requiring hardware or software changes.
It is a still further advantage of the present invention that system information, such as tachometer calibration, overspeed and underspeed setpoints, and engine run hours are stored in nonvolatile memory. This ensures no data is lost, even when backup batteries are replaced.
The system according to the present invention may be implemented using a low power microprocessor programmed to carry out operations corresponding to the components described herein.